Decarbonisation of service vessels in offshore wind power through power-to-X self-sufficiency

Abstract: This report examines the possibilities of decarbonising operation & maintenance vessels for a prospective floating offshore wind power park at the Utsira Nord site in Norway, through self-sufficient energy carrier production utilizing power-to-X-solutions. Possible alternative fuels are identified as compressed hydrogen, batteries, liquid hydrogen, ammonia, methanol, and biofuels, out of which the former two are the subject for thorough investigation in this report. The effects of an in-park electric charging buoy are also investigated. A literature study is conducted and projected technical properties for production, storage, and drivetrain for the year 2030 are compiled. Nine cases comprising drive trains for two vessel types – crew transfer vessels (CTV) and service operation vessels (SOV) -, production, and storage are constructed (including three base cases). Past and future electricity costs in Norway are analysed. Net present costs, levelized cost of energy (LCOE) of hydrogen, and fuel cost per MWh vessel output are determined. The global warming potential on a life cycle basis for components and energy use are determined. For CTVs, hydrogen is viable for short transits and battery solutions are not viable, as vessel mass and volume capacities are too low. For SOVs, battery systems are viable when combined with a charging buoy, hydrogen systems are viable regardless but also benefits from implementation of a charging buoy. Hydrogen solutions are 2.9 to 4.0 times more costly than the base cases, and battery-electric solutions are 7.0 times more costly. Global warming potential is reduced to 0.17 to 0.05 of the base cases, with hydrogen solutions performing the best. The inclusion of a charging buoy has potential to be a cost effective GWP abatement method.